Effect of aspirin on collateral blood flow after experimental thrombosis of the feline aorta.

In 11 cats, the caudal aorta was occluded with a thrombus to inhibit opening of collateral vessels to the hindlimbs. Five cats were not treated, and 6 cats were given aspirin (650 mg, orally) 1 hour before aortic occlusion. Before the aortas were occluded, platelet counts were measured in the 11 cats, and platelet aggregation by adenosine diphosphate was assessed in 4 cats scheduled for aspirin treatment. Cats were maintained for 3 hours after surgery, and the tests were repeated. In addition, serum salicylate concentrations were determined for all aspirin-treated cats. Collateral circulation was assessed as the time necessary for contrast media to appear in the iliac arteries caudal to the thrombus during aortography. Platelet counts were significantly (P less than or equal to 0.05) reduced in nontreated cats, but not in the aspirin-treated cats. Serum salicylate concentrations indicated that aspirin had reached therapeutic blood concentrations. Inhibition of adenosine diphosphate-induced platelet aggregation was observed in all postthrombosis aspirin-treated cats. Contrast media did not appear in the iliac arteries of nontreated cats until 7.5 +/- 0.5 s after injection. In all aspirin-treated cats, contrast media appeared in the iliac arteries within 2.3 +/- 0.3 s after injection. Platelet thromboxane A2 may be the factor promoting collateral inhibition after aortic thrombosis in cats.